This invention relates to dishwashing machines, and more particularly to a drain filter for preventing passage of hard or oversized articles into the drain and drain pump.
Conventional dishwashing machines replace the wash and rinse fluids several times during a cleaning cycle. For each fill, the fluid is first supplied to the dishwashing machine tank, then recirculated and sprayed onto the dishes, and then drained, to be followed several times again by the same sequence.
As the fluid is recirculated, it is filtered by a fine screen to prevent recirculation and redeposition of food particles back onto the dishes. Then as the fluid is drained, it is desirable to flush and drain away as much of the food items and debris as possible before refilling with fresh water. However, it is clearly not satisfactory to flush all of the soil items into the drain and drain pump. Some items may be too large or too hard (such as bones) for safe passage into the sewage system to which the drain is connected, and they might also damage the drain pump impeller.
A relatively coarse drain filter is therefore located over the entrance to the drain to stop such items. The openings through the drain filter are much larger than the openings in the fine screen filter so that much of the debris stopped by the latter can pass through the drain filter and be flushed down the drain.
Unfortunately, size alone is not a sufficient basis for separating drainable solids from those which should not be drained. Thus, cherry and olive pits, toothpicks, and broken pieces of glass and china, which may be quite small, clearly should not be permitted to enter the drain since they could damage the drain pump impeller. On the other hand, large bread crumbs and other soft food items can be safely passed through the drain, the drain pump, and the sewage system, and should therefore be removed even though they may be rather large. This therefore calls for some type of dynamic separation based on more than mere size discrimination.
Finally, the drain filter should be easily accessible to the machine operator so that the debris which it has stopped can be removed after the dishes have been cleaned.